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111.
112.
Tri(N-pyrrolyl)phosphine reacted with the sigma/pi complex [Pd(mu-Cl)(COD-MeO)]2 to give the octa-cycle [Pd(mu-Cl)[P(pyrl)3]]8 containing four Pd(I)-Pd(I) unbridged bonds.  相似文献   
113.
tRNA sulfurtransferase activity was assayed in Escherichia coli cell extracts obtained from bacterial suspensions exposed to a sub-lethal dose of ultraviolet-A radiation (fluence 148 kJ m(-2)) imparted at a low fluence rate (41 W m(-2)). We found that the irradiation reduced the enzymatic activity to one fourth of the control value, indicating that ultraviolet-A exposure inhibits the synthesis of 4-thiouridine, the most abundant thionucleoside in E. coli tRNA. Changes in the tRNA content of 4-thiouridine and its derived photoproduct 5-(4'-pyrimidin 2'-one) cytosine were studied in bacteria growing under ultraviolet-A irradiation. In these conditions the accumulation of photoproduct was limited, and the kinetics of this process was non-coincident with disappearance of 4-thiouridine. The results, which are compatible with the fact that ultraviolet-A induces an inhibition of the 4-thiouridine synthesis, suggest that the effect of radiation on tRNA modification is relevant to tRNA photo-inactivation in growing bacteria.  相似文献   
114.
[CuBr2(2,2'-bipyridine)] catalyses the selective and very mild aerobic oxidation of primary alcohols to aldehydes in acetonitrile:water (2:1) in the presence of 2,2,6,6-tetramethylpiperidinyl-1-oxy (TEMPO) and a base as cocatalysts.  相似文献   
115.
The amount of sample that is available for analysis in laboratory plant cultivation experiments is usually very limited. Highly sensitive analytical techniques are therefore required, even for elements that are present in the plants at mg g–1 concentrations, and graphite furnace atomic absorption spectrometry (GFAAS) was chosen in this work because of its micro-sampling capability, and its relatively simple operation. Four micro-methods were investigated for the determination of iron in roots and leaves of rice plants: i) a micro-digestion with nitric and hydrochloric acids, ii) a slurry procedure using tetramethylammonium hydroxide (TMAH) tissue solubilizer, iii) a slurry prepared in 1.4 mol L–1 nitric acid, and treated in an ultrasonic bath, and iv) the direct analysis of solid samples. The micro-digestion was suffering from high blank values and contamination problems, so that it could not be recommended for routine purposes. The TMAH method exhibited poor precision and occasional low recoveries, particularly for real samples. Direct solid sampling analysis gave results similar to those obtained with the slurry technique with ultrasonic agitation for the determination of iron in certified reference materials with iron content up to about 100 g g–1, but was too sensitive for the investigated rice plants, which had an iron content up to several mg g–1. The slurry technique with ultrasonic treatment of the samples, suspended in dilute nitric acid, was finally adopted as the method of choice.The method was then applied for the determination of iron in the leaves and in different compartments of the roots of two rice cultivars, one sensitive to iron toxicity, an important nutritional disorder, and the other one resistant to iron toxicity. The results suggest that the higher resistance to iron toxicity of the second cultivar is due to a smaller uptake of iron from the soil, resulting in lower iron levels in all compartments of the plant.  相似文献   
116.
117.
This paper is concerned with the application of two possible definitions of rank to certain well-known semigroups.AMS Subject Classification (2000), 20M10  相似文献   
118.
We construct a large family of complete maximal surfaces in the static Robertson–Walker 3-spaces with negative base curvature. These examples provide a wide variety of non-standard foliations of such spaces by entire maximal graphs.  相似文献   
119.
120.
A series of gradient and block copolymers, based on 2‐(2‐methoxyethoxy)ethyl methacrylate (MEO2MA) and tert‐butyl acrylate (tBA), were synthesized by atom transfer radical polymerization (ATRP) in a first step. The MEO2MA monomer leads to the production of thermosensitive polymers, exhibiting lower critical solution temperature (LCST) at around room temperature, which could be adjusted by changing the proportion of tBA in the copolymer. In a second step, the tert‐butyl groups of tBA were hydrolyzed with trifluoroacetic acid to form the corresponding block and gradient copolymers of MEO2MA and acrylic acid (AA), which exhibited both temperature and pH‐responsive behavior. These copolymers showed LCST values strongly dependent on the pH. At acid pH, a slightly decrease of LCST with an increase of AA in the copolymer was observed. However, at neutral or basic conditions, ionization of acid groups increases the hydrophilic balance considerably raising the LCST values, which even become not observable over the temperature range under study. In the last step, these carboxylic functionalized copolymers were covalently bound to biocompatible and biodegradable films of poly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate) [P(HB‐co‐HHx)] obtained by casting and, previously treated with ethylenediamine (ED) to render their surfaces with amino groups. Thereby, thermosensitive surfaces of modified P(HB‐co‐HHx) could be obtained. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011  相似文献   
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